In hybrid vehicles, which can be driven both by electromotors only and which, in hybrid operation, additionally also use a combustion engine for driving the vehicle, the combustion engine must first be started in the transition from electric-only operation to hybrid operation. Such hybrid vehicles are typically equipped with a hybrid clutch, which couples the driven shafts of the electromotor and the combustion engine. As a rule, the hybrid clutch is embodied in the form of a sliding clutch or as a proportional clutch. A proportional clutch is a clutch, which, in contrast to a shift-only clutch, is able to set a desired transmitted torque, for instance according to a suitable manipulated variable.
To drag the combustion engine, the hybrid clutch is activated during the electric driving, so that a corresponding specific transmitted torque is transmitted to the combustion engine, and the combustion engine is started. Prior to complete, autonomous running of the combustion engine there is temporary slippage at the hybrid clutch between the stationary or starting combustion engine and the electromotor rotating at a specific engine speed.
In an rpm-regulated electromotor, a torque for starting the combustion engine is transmitted as transmitted torque in the transition from electric-only operation to hybrid operation. The torque picked up by the combustion engine via the hybrid clutch interferes with the closed-loop speed control, thereby causing a considerable system deviation from the setpoint speed, i.e., a drop in the instantaneous engine speed. The driver of the vehicle perceives this as a strong jerk.